In recent years, an electronic key system has been incorporated into leisure vehicles such as motorcycles, which are open to the outside, as in general automobiles. As used herein, the term “leisure vehicles” refers to vehicles that are open to the outside, such as motorcycles, three-wheeled vehicles, all terrain vehicles, utility vehicles, personal watercraft, or snowmobiles.
In such electronic key systems, a user need not insert a key into a key hole of a main switch for locking or unlocking. When the user carrying in a pocket or the like a portable device capable of transmitting/receiving data comes closer than a predetermined distance away from the leisure vehicle, an unlocking operation or an ON-operation of the main switch is carried out, whereas when the user comes farther than the predetermined distance away from the leisure vehicle, a locking operation or an OFF-operation of the main switch is carried out. Thus, the electronic key system is convenient to the user.
In cases where a user of a motorcycle equipped with the above described electronic key system puts the portable device on a fuel tank, a bag, or the like for a moment and then pays money in a gas station or a tollbooth of a toll road, the portable device will fall off to the ground and will be lost if the user starts the motorcycle without noticing that the portable device is left thereon. In other cases where the user puts money out of and into a wallet in the gas station or in the tollbooth, the user may drop the portable device from the pocket or the like by mistake.
Japanese Laid-Open Patent Application Publication No. 2005-335675 discloses an electronic key system equipped in the leisure vehicle which is intended to avoid the loss of a portable device. This electronic key system is configured so that an electronic key controller built into the vehicle transmits a confirmation signal at predetermined time intervals, and a portable device is configured to transmit a response signal to the electronic key controller upon receiving the confirmation signal from the electronic key controller. Based on the received response signal, the electronic key controller confirms that the portable device is not lost. On the other hand, when the electronic control controller does not receive the response signal, it determines that the portable device has been lost, and causes an alarm to be raised to inform a user (or rider) of the loss of the portable device.
In the above electronic key system, since a battery built into the portable device has a small capacity, the portable device transitions from a sleep mode to an active mode upon receiving the confirmation signal so that consumption of battery power is reduced. However, life of the battery in the above electronic key system is still short, and therefore would be desirable to extend.